1. Field Of The Invention
This invention relates generally to fluid pressure brake and analogous systems and more specifically to those of the inertia control type including brake system control by plural cooperating sensing means producing a single signal.
2. Description Of The Prior Art
Vehicle wheel speed sensors are generally of two basic types. One type includes those having a rotor and stator with axial spacing therebetween and another type includes those having a rotor and stator with radial spacing therebetween. The axially spaced rotor-stator can be further divided into those which are commonly referred to as point sensors and those which include a continuous sensing arrangement. The continuous sensing arrangement has recently been extended to the radially spaced rotor-stator.
A critical area of concern in such sensors is guarding signal irregularities caused by variations in the spacing between the rotor and stator. Such variations are due to inherent axial and radial flexures and oscillations as the wheel rotates about the axle resulting in flexures and oscillations as the rotor relative to the stator. Many sensor arrangements have attempted to overcome this problem.
One such sensor is disclosed in U.S. Pat. No. 3,683,219. This sensor can generally be classified as an axially spaced rotor-stator arrangement of the continuous sensing type. That is, the rotor and stator are in continuous annular electrical relationship as the annular rotor rotates relative to an annular stator. To overcome the problem of rotor-stator spacing variations, U.S. Pat. No. 3,683,219 axially spaces its tooth stator and rotor members with countercontacting friction bearing coatings urged into contact by a resilient member. However, there would appear to be undesirable wear and temperature problems associated with such countercontacting arrangements.
Another approach is disclosed in U.S. Pat. No. 3,812,391. The sensor of this patent can generally be classified as an axially spaced rotor-stator arrangement of the point sensor type. That is, a stator and rotor are in electrical association at a point during rotation of the rotor where the annular rotor passes in proximity to a stator unit mounted on an axle. To overcome the problem of rotor-stator spacing variations, U.S. Pat. No. 3,812,391 restricts axial flexure of the rotor by guiding that rotor between fixed guides axially spaced apart slightly more than the rotor thickness. Such arrangement appears to permit axial flexures and oscillations although limited by the guides.
As a result of the flexure of the oscillation problems of the axially spaced sensor devices, radially spaced rotor-stator arrangements have been disclosed. One such approach to radially spaced sensors is disclosed in U.S. Pat. No. 3,626,226 wherein a point type sensor is in radially spaced electrical association with a rotor at a point during rotation of the rotor where the annular rotor passes in proximity to a stator unit. However, radial flexures and oscillations would appear to cause the aforementioned signal variations.
An apparent satisfactory solution to sensor flexure problems would appear to be disclosed in radially spaced sensors wherein there is a continuous electrical association between an annular rotor and stator such as that described in the above-mentioned, cross-referenced, related applications. In such radially spaced sensors, the concentric association between rotor and stator are self-compensating inasmuch as radial flexures which cause a decrease in radial spacing at any point between rotor and stator cause a corresponding inherent increase in radial spacing at a point 180.degree. diametrically opposed to the point of decrease. Thus signal variations caused by the decreased spacing are countered by compensating signal variations caused by the inherent increased spacing.
Although radially spaced continuous sensors appear continuous sensors are generally necessarily more complex and expensive than point type sensors. It would therefore be advantageous to have a novel point sensor of the radially spaced type providing the advantages of simplicity, economy and self-compensating reliability.